Optimization of packet transmission paths

ABSTRACT

A method is disclosed for optimizing packet transmission paths in a mobile communication network ( 400 ) in which packets are transmitted and received between mobile stations ( 10 - 14 ) or between a mobile station and a fixed network ( 120 ) by way of a plurality of packet transmission device ( 60 - 64, 70 - 72, 80 , and  81 ) and radio base stations ( 50 - 57 ). When a mobile station uses a service that is provided by a fixed network ( 300 ), imposed are applied on the packet transmission path such that packets pass by way of specific packet transmission devices ( 80  and  81 ) depending on the fixed network (external network)  300 . When the mobile station uses a service that is provided by the mobile communication network ( 400 ), on the other hand, no restrictions are imposed on the packet transmission path, and the packet transmission path is thus set such that the link costs are a minimum.

TECHNICAL FIELD

The present invention relates to a method of setting paths of packetcommunication in a mobile communication network, and more particularlyto a method of optimizing packet transmission paths in a network inwhich a plurality of packet transmission devices and radio base stationsare connected in a hierarchy.

BACKGROUND ART

Typically, a packet mobile communication network requires theunobstructed call origination from mobile stations, call termination tomobile stations, and continuation of packet communication that is inprogress despite the movement of the mobile stations within the network.For this reason, information such as the positions of mobile stationsand the closest radio base station is constantly managed and updated asnecessary in a packet mobile communication network. When the number ofmobile terminals that are managed in a portable telephone system isextremely large, the centralized management of information of eachindividual mobile station leads to an increase in the amount ofmanagement traffic that must be transferred inside the network, and inaddition, results in considerable time expended for the switching ofpacket transmission paths that accompanies movement. For this reason,techniques are typically employed wherein packet transmission devicesand positional management servers are normally arranged hierarchically,and the managed traffic for movement within each hierarchy is localizedwithin the hierarchy.

In the case of a mobile communication network based on, for example, thespecifications of the GPRS (General Packet Radio Service) of 3GPP (3rdGeneration Partnership Project), the packet transmission device of thehighest level is referred to as the GGSN (Gateway GPRS Support Node),the packet transmission device of the next level is referred to as theSGSN (Serving GPRS Support Node), the packet transmission device of thenext level is referred to as the RNC (Radio Network Controller) or BSC(Base Station Controller), and the radio base stations are arranged atthe lowest level. The packet communication scheme in the GPRS isdescribed in detail in the technical specification 3GPP TS 23.060,“General Packet Radio Service (GPRS); Service Description; Stage 2.”

In GPRS, when mobile stations are normally connected to an outsideservice provider, packet communication is performed, the followingprocedures are taken:

1. The mobile station selects the radio base station for whichcommunication conditions are best and establishes a data link.

2. The mobile station establishes a data link to the RNC/BSC to whichthe radio base station belongs.

3. The mobile station establishes a data link to the SGSN to which theRNC/BSC belongs.

4. The mobile station reports to the SGSN the name of the serviceprovider to which it is requesting connection. This name is referred toas the APN (Access Point Name).

5. The SGSN selects the appropriate GGSN in accordance with the reportedAPN and the subscriber information of the mobile station, andestablishes a data link between the SGSN and the GGSN.

6. The mobile station begins to communicate packets with the outsideservice provider by way of the radio base station, the RNC/BSC, theSGSN, and the GGSN that have been determined in this way.

7. When the mobile station moves during communication, communication iscontinued by appropriately reselecting the connecting radio basestation, RNC/BSC, and SGSN.

8. When communication is completed, the mobile station releases each ofthe data links.

In this way, when a mobile station connects to a service provideroutside the mobile communication network in GPRS, and performs packetcommunication, the packet transmission path within the mobilecommunication network is substantially optimized. This is because thenode to an outside service provider is fixed in the GGSN that is at theapex of the hierarchy of packet transmission devices. A similar type ofhierarchical architecture is also employed in packet mobilecommunication systems other than GPRS.

However, constraints that force the transmission path to pass by way ofthe apex of the hierarchy of packet transmission devices when thecommunication partner of a mobile station is within the same mobilecommunication network results in the problem of redundancy in the packettransmission path. For example, in a packet communication services suchas voice communication or instant messaging, the bulk of traffic isbetween mobile stations that are at relatively close positions withinthe same mobile communication network. Even though the packettransmission path is optimized if packets are returned at packettransmission devices that are at a low level in the hierarchy at thistime, when the packet transmission path is restricted such that thepackets pass by way of the packet transmission device that belongs tothe highest-ranked level, network resources are needlessly consumed. Insome services that are used by the mobile station, moreover, failure toroute packets by way of a specific packet transmission devices may causeproblems relating to levying charges i.e., optimization of packettransmission paths cannot always be achieved.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a packettransmission path optimization method that relates to packet datacommunication in a mobile communication network for optimizing thepacket transmission path of packets according to the service that isused by a mobile station and according to the communication partner ofthe mobile station.

In the first packet transmission path optimization method according tothe present invention, in a mobile communication network fortransmitting and receiving packets between a mobile station and anothermobile station or fixed station by way of a plurality of packettransmission devices and radio base stations, a packet transmission pathis selected either by imposing restrictions on the packet transmissionpath such that packets pass by way of one or more specific packettransmission devices according to the type of service (such as anexternal network connection or Peer-to-Peer connection) that is used bythe mobile station, or by not imposing restrictions on the packettransmission path such that the sum of link costs is minimized.

In the second packet transmission path optimization method according tothe present invention, in a mobile communication network fortransmitting and receiving packets between a mobile station and anothermobile station or a fixed station by way of a plurality of packettransmission devices and radio base stations, the packet transmissionpath is optimized either by imposing restrictions on the packettransmission path such that packets pass by way of one or more specificpacket transmission devices when the mobile station uses a service (suchas a mail service, a Web browsing service, or a service for downloadingmusic/movie files) that is provided by an external network, or by notimposing restrictions on the packet transmission path such that the sumof link costs is minimized when the mobile station uses a service (suchas a voice telephone service, video telephone service, short message, orchat service) that is provided by the mobile communication network towhich the mobile station is directly connected.

In the third packet transmission path optimization method according tothe present invention, when the radio base stations or packettransmission devices to which a mobile station is connected change dueto movement of the mobile station in the first or second packettransmission path optimization method, if there is a plurality ofspecific packet transmission devices through which packets are to pass,and if the sum of link costs is less for a packet transmission path thatpasses by way of specific packet transmission devices other than thespecific packet transmission devices that were selected before movement,restrictions are imposed on the packet transmission path by againselecting the other specific packet transmission devices.

In the fourth packet transmission path optimization method according tothe present invention, in a mobile communication network fortransmitting and receiving packets between a mobile station and anothermobile station or a fixed station by way of a plurality of packettransmission devices and radio base stations that are connectedhierarchically after a packet transmission device has designated inadvance a portion or all of the packet transmission path, wherein apacket transmission device, when designating the packet transmissionpath, selects either a route that passes by way of packet transmissiondevices that belong to a higher-ranked level than its own level or aroute that passes by way of only packet transmission devices that belongto lower-ranked levels than its own level such that the sum of linkcosts is lower and then establishes the packet transmission path.

In the fifth packet transmission path optimization method according tothe present invention, in a mobile communication network fortransmitting and receiving packets between a mobile station and anothermobile station or a host that is connected to an external network by wayof a plurality of packet transmission devices and radio base stationsthat are connected hierarchically after a portion or all of the packettransmission path has designated in advance, when a packet transmissiondevice that belongs to a higher-ranked level detects after the packettransmission path has been established that a packet transmission pathhaving a lower sum of link costs can be established in a lower-rankedlevel than its own, the packet transmission device of the higher-rankedlevel instructs switching of the packet transmission path from packettransmission devices of the higher-ranked level to packet transmissiondevices of the lower-ranked level such that a packet transmission pathis established between packet transmission devices of the lower-rankedlevel.

According to the sixth packet transmission path optimization methodaccording to the present invention, when a packet transmission device ofa higher-ranked level instructs switching of a packet transmission pathto packet transmission devices of a lower-ranked level in the fifthpacket transmission path optimization method, the packet transmissiondevice of the higher-ranked level transfers communication contexts thatis possesses such as charge information or authentication informationfor mobile stations to the packet transmission device of thelower-ranked level.

According to the seventh packet transmission path optimization methodaccording to the present invention, in a mobile communication networkfor transmitting and receiving packets between a mobile station andanother mobile station or a host that is connected to an externalnetwork by way of a plurality of packet transmission devices and radiobase stations that are hierarchically connected after a portion or allof the packet transmission path has been designated in advance, when theradio base stations or packet transmission devices to which a mobilestation is connected change due to movement of the mobile station afterthe packet transmission path has been established, a packet transmissiondevice of a higher-ranked level determines whether the packettransmission path can be changed to a packet transmission path thatpasses by way of packet transmission devices of a more highly-rankedlevel, and if a packet transmission path having lower costs can beestablished by way of packet transmission devices of the morehighly-ranked level, the packet transmission device of the higher-rankedlevel instructs switching of the packet transmission path to the packettransmission devices of the more highly-ranked level.

According to the eighth packet transmission path optimization methodaccording to the present invention, when the packet transmission deviceof a higher-ranked level instructs switching of the packet transmissionpath to the packet transmission devices of a more highly-ranked level inthe seventh packet transmission path optimization method, the packettransmission device of the higher-ranked level transfers communicationcontexts that it possesses such as charge information and authenticationinformation for mobile stations to the packet transmission device of themore highly-ranked level.

According to the ninth packet transmission path optimization methodaccording to the present invention, the mobile communication network inthe first to eighth packet transmission path optimization methods is aGPRS (General Packet Radio Service) network based on the TS 23.060standards of the 3GPP (Third Generation Partnership Project), the packettransmission devices of the highest-ranked level are GGSN (Gateway GPRSSupport Nodes), the packet transmission devices of the next level areSGSN (Serving GPRS Support Nodes), the packet transmission devices ofthe next level are BSC (Base Station Controllers) or RNC (Radio NetworkControllers), radio base stations are arranged at the lowest-rankedlevel, and routers are arranged as necessary between the radio basestations and the packet devices of each level.

According to the tenth packet transmission path optimization methodaccording to the present invention, the mobile communication network inthe first to eighth packet transmission path optimization methodsaccording to the present invention is a network based on the RFC(Request for Comments) 3220 Standards of the IETF (Internet EngineeringTask Force), the packet transmission devices of the highest-ranked levelare HA (Home Agents), radio base stations are arranged on thelowest-ranked level, and routers, which are the packet transmissiondevices of the intermediate levels, are arranged between the HA and theradio base stations.

According to the eleventh packet transmission path optimization methodaccording to the present invention, when packets are transmitted from acommunication partner of a mobile station to the mobile station in thetenth packet transmission path optimization method, the packettransmission path is selected by implementing tunneling and reversetunneling such that a HA is included in the packet transmission pathaccording to the type of service that the mobile station uses or by notimposing restrictions on the packet transmission path such that the sumof link costs is minimized

The first packet transmission device according to the present inventionincludes: means for identifying the type of service that the mobilestation is to use based on information that is included in a request toestablish a path that has been transmitted by the mobile station; andmeans for optimizing the packet transmission path either by imposingrestrictions on the packet transmission path such that the route passesby way of one or more specific packet transmission devices depending onthe type of service that has been identified or by not imposingrestrictions on the packet transmission path such that the sum of linkcosts is minimized.

The second packet transmission device according to the present inventionincludes: means for identifying, based on information that is includedin the request to establish a path that has been transmitted by a mobilestation, whether the mobile station is to use a service that is providedby an external network or the mobile station is to use a service that isprovided by the mobile communication network to which the mobile stationis directly connected; and means for setting the packet transmissionpath either by imposing restrictions on the packet transmission pathsuch that the packet transmission path passes by way of one or morespecific packet transmission devices when the mobile station is to use aservice that is provided by an external network, or by not imposingrestrictions on the packet transmission path such that the sum of linkcosts is minimized when the mobile station is to use a service that isprovided by the mobile communication network to which the mobile stationis directly connected.

The third packet transmission device according to the present inventionincludes means for, when the radio base stations or packet transmissiondevices to which the mobile station is connected change due to movementby the mobile station in the first or second packet transmission device,if there are a plurality of specific packet transmission devices throughwhich packets are to pass, and if a packet transmission path that passesby way of specific packet transmission devices other than the specificpacket transmission devices that were selected before the movement has alower sum of link costs, imposing restrictions on the packettransmission path by reselecting the other specific packet transmissiondevices.

The fourth packet transmission device according to the present inventionincludes: means for, when a portion or all of a packet transmission pathhas been designated in advance, selecting either a packet transmissionpath that passes by way of packet transmission devices that belong to alevel that is more highly ranked than its own or a packet transmissionpath that passes by way of only packet transmission devices that belongto levels that are ranked equal to or lower than its own depending onwhich path has the lower sum of link costs; and means for establishingthe selected packet transmission path.

The fifth packet transmission device according to the present inventionincludes: means for, after a packet transmission path has once beenestablished, detecting whether a packet transmission path having lowerlink costs can be established between packet transmission devices of alower-ranked level; and means for instructing packet transmissiondevices of a lower-ranked level to switch the packet transmission pathsuch that a packet transmission path is established between packettransmission devices of the lower-ranked level.

The sixth packet transmission device according to the present inventionincludes means for, when instructing switching of the packettransmission path in the fifth packet transmission device, transmittingcommunication contexts such as charge information and authenticationinformation for mobile stations to the packet transmission device of alower-ranked level.

The seventh packet transmission device according to the presentinvention includes: means for, when the radio base stations or packettransmission devices to which a mobile station is connected change dueto movement of the mobile station after a packet transmission path hasonce been established, determining whether the packet transmission pathcan be changed to pass by way of packet transmission devices of a levelthat is more highly-ranked than its own; and means for instructing thepacket transmission devices of the more highly-ranked level to switchthe packet transmission path when it has been determined that a packettransmission path can be established that passes by way of the packettransmission devices of the more highly-ranked level and that has alower sum of link costs.

The eighth packet transmission device according to the present inventionincludes in the seventh packet transmission device means for, wheninstructing switching of the packet transmission path, transferringcommunication contexts such as charge information or authenticationinformation for mobile stations to the packet transmission device of themore highly-ranked level.

According to the present invention, when a request to establish a pathor a request to alter a path is received from a mobile station, the typeof service that is used by the mobile station is first identified,following which, depending on the type of service that has beenidentified or the network that provides the service, the packettransmission path is optimized by imposing restrictions such that thepacket transmission path passes by way of one or more specific packettransmission devices, or by not imposing restrictions on the packettransmission path such that the sum of link costs is minimized. In thisway, the arrangement of route restrictions can be maintained inaccordance with services while raising the efficiency of utilization ofnetwork resources.

In addition, when altering a packet transmission path that has once beenestablished, the transfer of communication contexts such as theauthentication/charge information between the packet transmissiondevices of different levels allows an acceleration of thereestablishment of the packet transmission path.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of the configuration of a mobile communicationnetwork in which to the present invention has been applied;

FIG. 2 is a diagram of a second-level packet transmission device in thefirst embodiment of the present invention;

FIG. 3 is a diagram showing the configurations of a first-level packettransmission device and a third-level packet transmission device in thefirst embodiment;

FIG. 4 is a sequence chart of the initial authentication and positionregistration of a mobile station in the first embodiment;

FIG. 5 is a chart of the sequence when a mobile station connects to afixed network and establishes a packet transmission path in the firstembodiment;

FIG. 6 is a flow chart showing the operations when a second-level packettransmission device establishes a packet transmission path in the firstembodiment;

FIG. 7 is a chart of the sequence when a mobile station connects with amobile station and establishes a packet transmission path in the firstembodiment;

FIG. 8 is a chart of the sequence when a mobile station connects with amobile station and establishes a packet transmission path in the secondembodiment of the present invention;

FIG. 9 is a flow chart showing the operations when a second-level packettransmission device establishes a packet transmission path in the secondembodiment;

FIG. 10 shows the configuration of a mobile station user authenticationinformation table that is held by a second-level packet transmissiondevice in the second embodiment;

FIG. 11 shows the configuration of a mobile station user chargeinformation table that is held by a second-level packet transmissiondevice in the second embodiment;

FIG. 12 is a chart of the sequence when a mobile station that isconnected to a fixed network alters the packet transmission path in thethird embodiment;

FIG. 13 is a flow chart showing the operations when a second-levelpacket transmission device alters the packet transmission path in thethird embodiment; and

FIG. 14 is a flow chart showing the operations when a second-levelpacket transmission device alters the packet transmission path in thethird embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an example of the configuration of a mobile communicationnetwork to which the present invention has been applied. This mobilecommunication network includes mobile communication network 400, fixednetwork 300, and Web server 120. Mobile communication network 400includes: mobile stations 10-14, radio base station 50-57, first-levelpacket transmission devices 80 and 81, second-level packet transmissiondevices 70-72, third-level packet transmission devices 60-64, positionmanagement server 110, and authentication/charge server 100. Mobilestations 10-14 are connected to radio base stations 50-57 by way oflinks L10-L15, respectively. Radio base stations 50-57 and third-levelpacket transmission devices 60-64 are connected by way of links L20-L27.Third-level packet transmission devices 60-64 and second-level packettransmission devices 70-72 are connected by way of links L40-L44.Second-level packet transmission devices 70-72 and first-level packettransmission devices 80-81 are connected by way of links L80-L82. Inaddition, second-level packet transmission devices 70 and 71 areconnected by way of link L50, and second-level packet transmissiondevices 71 and 72 are connected by way of link L51. Third-level packettransmission devices 60 and 61 are connected to each other by way oflink L30. Further, position management server 110 andauthentication/charge server 100 are connected to second-level packettransmission device 70 by way of links L60 and L70, respectively. Inaddition, routers (not shown) may be arranged as necessary betweenpacket transmission devices 80, 81, 70-72, and 60-64 and radio basestations 50-57 of each of the levels.

When mobile communication network 400 is, for example, a GPRS networkbased on the standards of TS 23.060 of 3GPP, packet transmission devices80 and 81 of the highest (first) level are GGSN, packet transmissiondevices 70-72 of the next (second) level are SGSN, packet transmissiondevices 60-64 of the next (third) level are BSC or RNC, and radio basestations 50-57 are the lowest level. Alternatively, when mobilecommunication network 400 is a network based on the standards of RFC3220 of IETF, packet transmission devices 80 and 81 of the highest(first) level are HA (Home Agents), radio base stations 50-57 arearranged on the lowest level, and routers composed of packettransmission devices 60-64 and 70-72 of the intermediate levels arearranged between HA and the radio base stations.

The packet transmission devices are divided between three levels inorder to allow hierarchical management of the positions of mobilestations 50-57 and hierarchical control of packet paths during movement.This approach is widely employed in mobile communication networks.Although three levels are shown in FIG. 1, the number of levels may bevaried according to the scale of the mobile communication network oraccording to the operating requirement of the network. In addition, aspreviously described, position management server 110 may also bearranged hierarchically, but since this component is not directlyrelated to the present invention, only one position management server isarranged for the sake of simplificity in FIG. 1.

Mobile communication network 400 having the above-describedconfiguration is connected to a fixed network 1 (300), which is anexternal network, by way of links L90 and L91 through first-level packettransmission devices 80 and 81, respectively. A plurality of links neednot be provided for connection to fixed network 300, one link beingadequate as a minimum. Although only one external network is connectedin FIG. 1, a plurality of external networks may be connected. In thiscase, the correlation between first-level packet transmission devices 80and 81 and the external network is uniquely defined in the system.Mobile stations 50-57 obtain information by means of server/clientcommunication from a dedicated server such as Web server 120 that isconnected to fixed network 300. Alternatively, mobile stations 50-57 canalso make direct peer-to-peer connections with other mobile stations todirectly exchange information. Reference numerals P1 and P2 in FIG. 1indicate examples of packet transmission paths that are set according tothe present invention when mobile stations make direct peer-to-peerconnections, and reference numerals P3-P5 indicate examples of packettransmission paths that have been set according to the present inventionwhen mobile stations communicate with Web server 120.

First Embodiment

FIG. 2 shows an example of the configuration of second-level packettransmission device 70. Packet transmission device 70 includes: packetreceiver F100, packet transmitter F101, packet transfer unit F102,charge information collection unit F103, control data type determinationunit F104, control data packet generation unit F105, routing table F106,control data processor F110, user information management table F120, andcontrol subroutine group F130. Upon receiving packets from the outside,packet receiver F100 performs a lower-layer termination process on thepackets and then supplies the packets to packet transfer unit F102.Packet transfer unit F102, upon receiving packet from packet receiverF100 or control data packet generation unit F105, consults routing tableF106 to determine the next-hop node of the packet, and if the packet isnot addressed to its own node, supplies the packet as output to theoutside from packet transmitter F101. Packet transfer unit F102, upondetecting a control packet that is addressed to its own node, suppliesthe packet to control data type determination unit F104. Packet transferunit F102 also measures the connection time and the amount of packetsthat are transferred for each mobile station by the method that isdesignated by charge information collection unit F103 and supplies theresults to charge information collection unit F103. Upon receiving acontrol packet, control data type determination unit F104 determines thetype of control data and supplies the result to control data processorF110.

According to the control data type, control data processor F110comprises the sub-blocks: position inquiry request/response unit F111,position registration request/response unit F112, path establishmentrequest/response unit F113, user authentication request/response unitF114, path disconnection request/response unit F115, and path alterationrequest/response unit F116. User information that is obtained by thetransmission and reception of control data is stored in user informationmanagement table F120. User information management table F120 containsuser position information F121, user authentication information F122,and user charge information F123. In addition, some of the internalprocessing of control data processor F110 is implemented by invokingvarious functions that are contained in control subroutine groups F130.User authentication information transfer processor F131 that iscontained in control subroutine group F130 carries out processing whenexchanging user authentication information with other packettransmission devices. User charge information transfer processor F132performs processing when exchanging user charge information with otherpacket transmission devices. Service type identification unit F134performs processing to determine the type of service when receiving pathestablishment/alteration request messages. Service provideridentification unit F133 performs processing to identify the internal oroutside business that provides a service when receiving a pathestablishment/alteration request message. Packet transfer pathcalculator F135 performs processing to calculate the optimum packettransmission path according to the type of service and the serviceprovider and to set this packet transmission path in routing table F106.Other packet transmission devices 71 and 72 in the second level alsohave the same configuration as packet transmission device 70 that isshown in FIG. 2.

FIG. 3 shows an example of the configuration of third-level packettransmission device 60 and first-level packet transmission device 80.Third-level packet transmission device 60 or first-level packettransmission device 80 has the configuration of second-level packettransmission device 70 that is shown in FIG. 2 with user positioninformation F121, service provider identification unit F133, and servicetype identification unit F134 eliminated. The other third-level packettransmission devices 61-64 and the other first-level packet transmissiondevice 81 also have the same configuration as packet transmissiondevices 60 and 80 that are shown in FIG. 3.

The operation of the mobile communication network of FIG. 1 will beexplained below.

Explanation first regards processing for authentication and positionregistration at the time of activating a mobile station taking mobilestation 10 as an example. FIG. 4 shows the sequence of messages forauthentication and position registration at the time of activatingmobile station 10. Mobile station 10 first searches for a radio basestation in the vicinity, transmits to radio base station 50 radio linkestablishment request M10, receives from radio base station 50 radiolink establishment response M11, and then establishes a radio link.Mobile station 10 next transmits user authentication request message M12to authentication/charge server 100, receives user authenticationresponse M13 from authentication/charge server 100, and then exchangesthe series of messages that are required for user authentication. Ifuser authentication is successful, mobile station 10 next transmitsposition registration request M14 to position management server 110,receives position registration response M15 from position managementserver 110, and registers its own position. This position registrationinformation is used for controlling the path when a call is terminatedto mobile station 10 from external network 300 or within mobilecommunication network 400. Upon completing the position registration,mobile station 10 transmits radio link disconnection request M16 toradio base station 50, receives radio link disconnection response M17from radio base station 50, and thus cuts the radio link and enters apower-saving mode.

Explanation next regards processing when a mobile station has connectedto an external network and started packet communication, taking mobilestation 14 as an example. FIG. 5 shows the sequence of messages up tothe time that mobile station 14 connects to the external network andbegins packet communication. Mobile station 14 first transmits radiolink establishment request message M20 to radio base station 56,receives a radio link establishment response from radio base station 56,and establishes a radio link between radio base station 56 andthird-level packet transmission device 63. Mobile station 14 nexttransmits path establishment request message M22 on the radio link thathas been established. If the mobile communication network is based onGPRS that is stipulated by 3GPP TS 23.060, path establishment requestmessage M22 is equivalent to a PDP Context Activation message that amobile station transmits to a SGSN. Alternatively, if the mobilecommunication network is based on Mobile IP that is stipulated by RFC3220 of IETF, path establishment request message M22 is equivalent to aRegistration Request message that is transmitted from a mobile stationto a home agent. The mobile communication network may also be based onan architecture other than the two described hereinabove. In pathestablishment request message M22, information is included that showsthat the connection destination is fixed network 300 (1), and that therequested service is an external network connection. Path establishmentrequest message M22 is transferred to first-level packet transmissiondevice 80 by way of radio base station 56, third-level packettransmission device 63, and second-level packet transmission device 71.First-level packet transmission device 80 responds to this message withpath establishment response message M23, and when this message istransferred to mobile station 14, packet transmission path P3 isestablished between mobile station 14 and first-level packettransmission device 80. Mobile station 14 subsequently uses this packettransmission path P3 and performs transfer of user data M24 with Webserver 120 that is connected to fixed network 300. If mobilecommunication network 400 is a network that is based on the standards ofRFC 3220 of the IETF, packet transmission device 80 is a HA, andtunneling and reverse tunneling are implemented when packets aretransmitted from the communication partner of the mobile station to themobile station.

FIG. 6 is a flow chart showing the operations when second-level packettransmission devices 70, 71, and 72 establish packet transmission paths.The following explanation regards the operations when a second-levelpacket transmission device establishes a packet transmission path,taking packet transmission device 71 as an example.

Second-level packet transmission device 71, upon receiving a pathestablishment request message from lower-level packet transmissiondevice 63 in Step S11, determines the type of service that is requestedin Step S12. When the requested service is an external networkconnection, one of packet transmission devices 80 and 81 is selected inaccordance with the external network of the connection destination inStep S13. In the case of the sequence that is shown in FIG. 5, theconnection destination is fixed network 300, and packet transmissiondevice 80 therefore has lower link costs from the standpoint of packettransmission device 71. As a result, packet transmission device 80 isselected and path establishment request information is transferred inStep S14, whereby the process is completed.

If the requested service is a peer-to-peer connection, on the otherhand, packet transmission device 71 obtains information of the area inwhich the mobile station that is the connection destination is locatedfrom position management server 110 in Step S15. The geographical rangethat this area information covers is determined according to thecircumstances of the operator of the mobile communication network, andthis range may be in units of radio base stations or of second- andthird-level packet transmission devices, or logical area informationthat is distinct from physical nodes may also be defined. Based on theacquired information of the area in which the mobile station is located,packet transmission device 71 next selects in Step S16 the packettransmission devices such that the packet transmission path passes byway of packet transmission device 71 and such that the sum of the linkcosts of the packet transmission path is a minimum. The link costs areeach set in advance by, for example, the link bandwidth and the line usecharges that are generated with use of links. When the “Next Hop” packettransmission device that is to be included in the packet transmissionpath is selected, a path establishment request message is transferred tothe selected packet transmission device in Step S17 and the process thuscompleted.

Regarding the distribution between packet transmission devices of costinformation for links that are not directly connected and the collectionof information relating to the peripheral network configuration and thepossibility of arrival of packet transmission paths, this informationmay be statically set in advance in packet transmission devices, or analready-existing routing protocol may be used. For example, according toOpen Shortest Path Find (OSPF), Version 2 that is stipulated by RFC 2328of the IETF, a method is shown in which link cost information isexchanged between packet transmission devices, and the Dijkstraalgorithm is used to calculate the minimum-cost path between any packettransmission devices. The link costs are basically values that arestatically determined by the business according to the bandwidth of eachlink, but may also change dynamically according to the link load or thenumber of mobile stations that are under the jurisdiction of the linkthat is managed by the position management server of the mobilecommunication network.

In addition, a conventional mobile communication network protocol maybeemployed as the method of selecting the packet transmission devicesthrough which the packet transmission path is to pass based on the nameor address of the external network that is to be connected whenestablishing a packet transmission path. For example, a method is shownin Appendix A (“APN and GGSN Selection”) of 3GPP TS 23.060 in which theGGSN though which the packet transmission path passes are selected inthe SGSN based on the name and address of the external network that isto be connected. Items that are reported from a mobile station to apacket transmission device such as a SGSN when establishing a packettransmission path in the present invention include the type of serviceand information of the network that provides service, in addition to thename and address of the external network that is to be connected thatare reported in the prior art. These items correspond to the informationthat is transmitted in message M22 in FIG. 5 and in messages M32 and M35in FIG. 7 that will be explained hereinbelow.

Explanation next regards the message sequence when establishing a packettransmission path between a mobile station and a mobile station usingthe establishment of a packet transmission path between mobile stations10 and 11 as an example. FIG. 7 shows the message sequence when mobilestation 10 connects to mobile station 11 and establishes a packettransmission path. Mobile station 10 transmits radio link establishmentrequest message M30 to radio base station 50, receives radio linkestablishment response M31 from radio base station 50, and establishes aradio link between radio base station 50 and third-level packettransmission device 60. Mobile station 10 next transmits pathestablishment request message M32 on the established radio link. Pathestablishment request message M32 contains information indicating thatmobile station 11 is the connection destination and that the requestedservice is a peer-to-peer connection. Path establishment request messageM32 is transferred by way of radio base station 50 and third-levelpacket transmission device 60 to second-level packet transmission device70.

Second-level packet transmission device 70, upon seeing the content ofpath establishment request message M32 that has been received andlearning that the requested service is a peer-to-peer connection andthat the connection destination is mobile station 11, sends positioninquiry message M33 to position management server 110 to ask forinformation of the area in which mobile station 11 is located. Whenresponse message M34 to this position inquiry is returned from positionmanagement server 110 in response to this message, packet transmissiondevice 70 learns that third-level packet transmission device 61 shouldbe made the “Next Hop” to decrease the sum of the link costs of thepacket transmission path and therefore transmits path establishmentrequest message M35 to third-level packet transmission device 61. Pathestablishment request message M35 contains information that indicatesthat the connection destination is mobile station 11 and that therequested service is a peer-to-peer connection.

Third-level packet transmission device 61, upon receiving pathestablishment request message M35 from second-level packet transmissiondevice 70, transmits radio link establishment request M36 to mobilestation 11, and after receiving radio link establishment response M37from mobile station 11 and establishing a radio link with mobile station11, transmits path establishment request message M38 to mobile station11. Path establishment request message M38 contains informationindicating that the connection destination is mobile station 11 and thatthe requested service is a peer-to-peer connection.

Mobile station 11 on the termination side returns path establishmentresponse message M39 in response to path establishment request messageM38, and the packet transmission path is established at the time thismessage arrives at mobile station 10 on the origination side. The packettransmission path that is established at this time is P1. Mobile station10 and mobile station 11 transfer user data M40 on packet transmissionpath P1 that has been established in this way.

In contrast to this packet transmission path P1, the packet transmissionpath that is set according to the prior art must pass by way of the apexof the levels of the packet transmission devices, meaning that aredundant packet transmission path is set that passes from mobilestation 10 to radio base station 50, to third-level packet transmissiondevice 60, to second-level packet transmission device 70, to first-levelpacket transmission device 80, to second-level packet transmissiondevice 70, to third-level packet transmission device 61, to radio basestation 52, and finally to mobile station 11.

Thus, in the present embodiment, a packet transmission path is selectedby either imposing restrictions on the packet transmission path suchthat the path must pass by way of a particular packet transmissiondevice according to the service or the position of the communicationpartner of the mobile station, or without imposing restrictions on thepacket transmission path such that the sum of the link costs isminimized. In other words, when a mobile station uses a service that isprovided by an external network, the selection of packet transmissiondevices depending on the external network that is the connectiondestination in Step S13 of FIG. 6 imposes restrictions on the packettransmission path such that the route will necessarily pass by way ofparticular packet transmission devices such as first-level packettransmission device 80 in the example of FIG. 5. On the other hand, whena mobile station uses a service that is provided by the mobilecommunication network to which the mobile station is directly connected,the packet transmission path is selected without imposing restrictionson the packet transmission path such that the sum of link costs is aminimum in Step S16 in FIG. 6. As a result, the present embodiment notonly maintains an arrangement of path restrictions that accord with theservice but can also maximize the efficiency of utilization of networkresources. This point is next explained in greater detail.

As an example, a case is considered in which an external networkconnection service is used for connecting to an outside fixed network byway of a first-level packet transmission device. The outside fixednetwork is an Internet service provider (ISP) or a business network. Inaddition, it is assumed that a particular fixed network “a” is connectedto a packet communication network through first-level packettransmission device A, and another fixed network “b” is connected to apacket communication network through first-level packet transmissiondevice B. When selecting the packet transmission path having the minimumlink costs, restrictions typically cannot be applied on the packettransmission path such that the route passes by way of specific packettransmission paths. Thus, when the mobile station of a subscriber of afixed network “a” uses an external network connection service, setting apath via packet transmission device B because this path has the minimumlink cost may cause the mobile station to establish communication with aserver that is on the Internet by way of fixed network “b,” with whichthe subscriber has no contract. This situation is not agreeable to fixednetwork “b,” which is the non-contracted Internet service provider. Thepresent embodiment, however, provides a solution to this type of problembecause the correlations between first-level packet transmission devicesA and B and external networks “a” and “b” are uniquely defined, and whena mobile station uses an external network connection service,restrictions are applied on the packet transmission path such that theroute must pass by way of a specific first-level packet transmissiondevice. On the other hand, in the case of a connection between mobilestations within the same packet communication network, the packettransmission path is set such that the sum of link costs is minimizedwithout imposing restrictions on the packet transmission path, wherebythe efficiency of utilization of the network link resources can beincreased.

Second Embodiment

Explanation next regards the second embodiment of the present inventionwith reference to FIG. 1 and FIGS. 8 to 11. Explanation next regardsprocessing for establishing a packet transmission path between mobilestations in the present embodiment, taking as example the establishmentof a packet transmission path between mobile station 10 and mobilestation 11. FIG. 8 is a message sequence when mobile station 10 connectswith mobile station 11 and establishes a packet transmission path in thepresent embodiment. Messages M50-M54 are similar to messages M30-M34 inFIG. 7 that was used in the explanation of the first embodiment.

Second-level packet transmission device 70, upon receiving informationof the area in which mobile station 11 is located from positionmanagement server 110, investigates whether the direct transfer ofpackets between third-level packet transmission devices 60 and 61, whichare lower-level packet transmission devices, enables a packettransmission path having link costs that are lower than a packettransmission path that passes through its own device, second-levelpacket transmission device 70. Then, upon learning that this type ofpacket transmission path can be established, second-level packettransmission device 70 transmits path alteration request message M55 tothird-level packet transmission device 60, instructs the establishmentof a packet transmission path that passes by way of third-level packettransmission device 61, and additionally, transfers to third-levelpacket transmission device 60 communication contexts that include, forexample, the authentication and charge information of mobile stations 10and 11 and that are held by second-level packet transmission device 70.Path alteration request message M55 includes communication contexts andinformation that indicates that the connection destination is mobilestation 11 and that the packet transmission device through which thepath passes is third-level packet transmission device 61.

In accordance with this message, third-level packet transmission device60 transmits path alteration response message M56 to second-level packettransmission device 70, and then transmits to third-level packettransmission device 61 path establishment request message M57 thatcontains information indicating that the connection destination ismobile station 11 and that the requested service is a peer-to-peerconnection. The subsequent messages M58 to M61 are equivalent tomessages M36 to M39 in FIG. 7 of the explanation of the previous firstembodiment. By means of these procedures, packet transmission path P2 isestablished between mobile station 10 and mobile station 11, and packetsare transmitted and received between mobile station 10 and mobilestation 11 by way of this packet transmission path P2.

At this point, an authentication operation is carried out by theprocedures that are shown in FIG. 4 before the mobile station initiatescommunication to determine whether this mobile station is already alegitimate user, and the result of authentication and the authenticationinformation are the authentication information for the mobile stationthat are held in packet transmission device 70. When packet transmissiondevice 60, which has received the transfer of the authenticationinformation from packet transmission device 70, receives a pathestablishment request or path alteration request from a user that hasnot yet been authenticated, packet transmission device 60 rejects therequest. Packet transmission device 60, which holds the authenticationinformation, distributes encryption keys to users that have completedauthentication and performs encrypted communication in links thatcontain radio intervals. In addition, charge information is used forgenerating a charge record according to the connection time of themobile station and the amount of packets that the mobile station hastransmitted and received. The authentication function and chargefunction must be supported in at least one packet transmission devicethat is contained in a packet transmission path. To this end, when theauthentication/charge functions are contained in a packet transmissiondevice that is not included in the packet transmission path as a resultof route optimization or the movement of a mobile station, thesefunctions must be handed over to a packet transmission device in the newpacket transmission path.

FIG. 9 is a flow chart showing the operations when second-level packettransmission devices 70, 71, and 72 establish a packet transmission pathin the second embodiment. Explanation next regards the operations whensecond-level packet transmission devices establish a packet transmissionpath taking packet transmission device 70 as an example.

Second-level packet transmission device 70, upon receiving a pathestablishment request message from lower-level packet transmissiondevices 60-62 in Step S21, first determines the type of requestedservice in Step S22. When the requested service is an external networkconnection, processing is carried out in Steps S23 and S24 that issimilar to Steps S13 and S14 in FIG. 6 that was used in the explanationof the first embodiment. On the other hand, when the requested serviceis a peer-to-peer connection, second-level packet transmission device 70acquires information of the area in which the mobile station that is theconnection destination is located from position management server 110 inStep S25, and then determines in Step S26 whether a packet transmissionpath having a lower sum of link costs than the link costs of the packettransmission path that passes by way of packet transmission device 70can be established between lower-level packet transmission devices. If apacket transmission path having a lower sum of link costs can beestablished between the lower-level packet transmission devices,second-level packet transmission device 70 selects in Step S27 thelower-level packet transmission device to which the packet transmissionpath is to be changed, and in Step S28, transmits a path alterationrequest message to the selected lower-level packet transmission device,and further, transfers communication context information. Then, in StepS29, when a path alteration response is received from the lower-levelpacket transmission device, the process is completed.

The processing of Steps S30 and S31 that is carried out when a packettransmission path having a lower sum of link costs could not beestablished between lower-level packet transmission devices in Step S26is equivalent to Steps S16 and S17 in FIG. 6 that was used in theexplanation of the first embodiment.

In this way, a path for transferring packets between mobile station 10and mobile station 11 was path P1 that passes by way of second-levelpacket transmission device 70 in the first embodiment. In the secondembodiment, however, path P2 is established at a level that is equal toor lower than the level of third-level packet transmission device 60,whereby a greater optimization of the packet transmission path isachieved.

FIG. 10 shows an example of the configuration of the user authenticationinformation table (corresponding to F122 in FIG. 2) that is managed bythe second-level packet transmission device. Mobile station identifierE10 is an identifier for uniquely identifying mobile stations. Finalauthentication time E11 indicates the time at which authentication waslast successful and is used for managing information on the timeremaining until starting the next authentication procedure.Authentication status E12 indicates whether the last authenticationprocedure succeeded or failed. Challenge random number E13 stores arandom number value that is used in the final authentication procedure.Authentication key E14 is key information for determining the success orfailure of the authentication of a mobile station. Encryption algorithmE15 is used when a different encryption is used for each mobile stationand holds the type of encryption algorithm such as AES (AdvancedEncryption Standard) and 3DES (Triple DES). Message encryption key E16is an encryption key that is used when actually encrypting user data.Message alteration detection key E17 is a key for detecting whether acontrol packet that is transmitted or received by a mobile station hasbeen tampered with. When authentication information of mobile stationsis transmitted between packet transmission devices in the secondembodiment, the necessary rows are extracted from among these items ofauthentication information and transferred.

FIG. 11 shows an example of the configuration of a user chargeinformation table (corresponding to F123 in FIG. 2) that is managed by asecond-level packet transmission device. Mobile station identifier E20is an identifier for uniquely identifying mobile stations. Service typeE21 indicates the type of service used by a mobile station, this itemtaking as input “external network connection” or “peer-to-peerconnection.” The type of service can be further subdivided according to,for example, the provided data rate or delay time. Connectiondestination E22 indicates the connection destination of a mobile stationand stores the identifier of a fixed network or mobile station. Uplinkdata transfer amount E23 and downlink data transfer amount E24 indicatein octet units the amount of data that has been transmitted or receivedby a mobile station in the uplink or downlink direction. Connection timeE25 holds in units of seconds the time from establishing a packettransmission path until disconnection. Mobile station location networkE26 indicates the network of a mobile communication business in which amobile station is located at the time of connection, and is chiefly usedfor charge control when roaming on the network of a business with whichthe mobile station is not directly contracted. When the chargeinformation of mobile stations is transferred between packettransmission devices in the second embodiment, the necessary rows areextracted from this charge information and transferred.

Third Embodiment

The third embodiment of the present invention will be explained belowwith reference to FIGS. 1, 12, 13, and 14.

The following explanation regards processing when the packettransmission path is changed in accordance with the movement of a mobilestation that is connected to a fixed network in the present embodiment,taking mobile station 14 as an example. FIG. 12 is a message sequencewhen mobile station 14 changes the packet transmission path whileconnected to fixed network 300. Mobile station 14 first connects toradio base station 56 by way of radio link L14 and transmits andreceives packet M70 with web server 120. The packet transmission path atthis time is P3 with radio base station 56, third-level packettransmission device 63, second-level packet transmission device 71, andfirst-level packet transmission device 80 interposed. When mobilestation 14 moves into the area of radio base station 57, mobile station14 transmits radio link establishment request M71 to radio base station57, receives radio link establishment response M72 from radio basestation 57, and establishes radio link L15. Next, when the connectingthird-level packet transmission device changes from packet transmissiondevice 63 to packet transmission device 64 with the change in radiolink, mobile station 14 transmits path alteration request message M73 topacket transmission device 64. Path alteration request message M73contains information indicating that the connection destination is fixednetwork 300 and that the requested service is external networkconnection. Third-level packet transmission device 64 transfers pathalteration request message M73 to second-level packet transmissiondevice 72. Second-level packet transmission device 72, upon receivingthis message, transmits position update request message M74 to positionmanagement server 110, and updates the information of the area in whichmobile station 14 is located.

Second-level packet transmission device 72 next compares packettransmission paths for connecting from mobile station 14 to fixednetwork 300 to determine which packet transmission path of packettransmission path P4 that passes by way of first-level packettransmission device 80 and packet transmission path P5 that passes byway of first-level packet transmission device 81 has the lower sum oflink costs. In this case, if it is assumed that switching to packettransmission path P5 provides a lower sum of link costs than packettransmission path P4, path alteration request message M76 is transmittedfrom second-level packet transmission device 72 to second-level packettransmission device 71. In addition, when determining whether the sum oflink costs is lower, a prescribed permissible range may be consideredwhereby, even though the sum of link costs may actually be lower, thesum of link costs is not determined to be lower if the amount of thisdecrease is within the permissible range.

In response to this message, second-level packet transmission device 71transfers communication contexts such as the authentication/chargeinformation of mobile station 14 to packet transmission device 72. Pathestablishment request message M78 is next transmitted from second-levelpacket transmission device 72 to first-level packet transmission device81, and upon the return of the response to this message, a new packettransmission path P5 that reaches from mobile station 14 to first-levelpacket transmission device 81 is established. Path establishment requestmessage M78 includes information that indicates that the connectiondestination is fixed network 300, and that the requested service is anexternal connection. Path disconnection request messages M81 and M83 arenext transmitted from second-level packet transmission device 72 topacket transmission devices 80, 71, and 63 on the previous packettransmission path P3, whereby this path is disconnected. Third-levelpacket transmission device 63 disconnects the radio link after packettransmission path P3 has been disconnected.

In the case of the prior art, on the other hand, there is no procedurefor reselecting a first-level packet transmission device, and as aconsequence, there is no transmission of path establishment request M78from second-level packet transmission device 72 to first-level packettransmission device 81 or of response message M79 from first-levelpacket transmission device 81 to second-level packet transmission device72 that are shown in the sequence shown in FIG. 12, nor is there anyaccompanying control. In the prior art, communication continues throughthe already selected first-level packet transmission device 80 despitemovement of mobile station 14. Thus, communication is performed usingpacket transmission path P4 even if, for example, packet transmissionpath P5 entails a lower sum of link costs than packet transmission pathP4.

FIG. 13 and FIG. 14 are flow charts illustrating the operations whensecond-level packet transmission devices 70-72 alter the packettransmission path in the third embodiment. Operations when asecond-level packet transmission device alters the packet transmissionpath will be explained below taking packet transmission device 72 as anexample.

Packet transmission device 72, upon receiving a path alteration requestmessage from a mobile station in Step S41, transmits a position updaterequest to position management server 110 and registers the new areainformation of the mobile station in Step S42. Upon receiving a positionupdate response message from position management server 110 in responseto this message in Step S43, packet transmission device 72 determinesthe type of service that is included in the path alteration requestmessage in Step S44. If the requested service is a peer-to-peerconnection, packet transmission device 72 determines in Step S45whether, by setting a packet transmission path that passes by way of alower-level packet transmission device that is not currently selected, apacket transmission path can be established that has a lower sum of linkcosts than the current packet transmission path. The state of thecurrent packet transmission path can be understood as follows:

First, packet transmission device 72 is able to know upon the arrival atpacket transmission device 72 of a path establishment request message ora path alteration request message that the originating packettransmission device and packet transmission device 72 itself areincluded in the packet transmission path. Further, if the requestedservice in the path establishment request message is a peer-to-peerconnection, packet transmission device 72 can specify the packettransmission device to which the mobile station that is the connectiondestination belongs by inquiring to the position management server forinformation of the area of location of the mobile station that is theconnection destination. An inquiry to the position management server isgenerated upon establishing a packet transmission path, but whenaltering an already established packet transmission path as in thepresent embodiment, new area information can be acquired from the packettransmission device that is the connection destination before alterationeven if an inquiry is not made to position management server 110.

If a packet transmission path can be established that entails a lowersum of link costs by passing by way of lower-level packet transmissiondevice, packet transmission device 72 newly selects lower-level packettransmission devices in Step S46 and proceeds to Step S47. If in StepS44 the service type is an external network connection, if thedetermination in Step S45 was “NO,” or if the process was completed inStep S46, packet transmission device 72 determines in Step S47 whether apacket transmission path having a lower sum of link costs can beestablished if the packet transmission path passes by way of ahigher-level packet transmission device that is not currently selected.If passage by way of a higher-level packet transmission device that isnot currently selected allows optimization of the packet transmissionpath, packet transmission device 72 newly selects the higher-levelpacket transmission device in Step S48. Next, packet transmission device72 determines in Step S49 whether the packet transmission device thatwas not currently selected has been selected. If a new selection has notbeen made, packet transmission device 72 simply transmits a pathalteration response message to the mobile station in Step S50 and thuscompletes the process. In this case, the packet transmission path thatwas requested by the path alteration request message continues to beused without alteration.

On the other hand, when a new packet transmission device is selected,packet transmission device 72 transmits path alteration requests topacket transmission devices on the previous packet transmission path inStep S51. In response to these requests, packet transmission device 72receives path alteration responses from the previous packet transmissiondevices in Step S52, whereupon packet transmission device 72 obtainscommunication context information from the packet transmission deviceson the previous packet transmission path in Step S53. Packettransmission device 72 then transmits path establishment requests to thenewly selected packet transmission devices in Step S54. In response tothese requests, packet transmission device 72 receives pathestablishment responses in Step S55, and then transmits a pathalteration response to the mobile station in Step S56. Finally, in StepS57, packet transmission device 72 transmits path disconnection requeststo the packet transmission devices that have been removed from thepacket transmission path. When packet transmission device 72 hasreceived path disconnection requests from all of the packet transmissiondevices that have been removed from the packet transmission path inresponse to these requests, the process is completed.

This determination of whether the packet transmission path should beswitched to pass by way of lower-level packet transmission devices orhigher-level packet transmission devices when a mobile station movesallows the optimization of the packet transmission path to the packettransmission path having the lowest sum of link costs.

When switching higher-level packet transmission devices in the thirdembodiment, the problem may arise that change of the layer-3 addressthat is assigned to the mobile station may cause disconnection of theapplication layer connection. To explain more specifically, a mobilecommunication network may in some cases pool layer-3 addresses for eachexternal network that is a connection destination in first-level packettransmission devices that serve as the gateways to external networks,and then dynamically assign layer-3 addresses in response to packetcommunication requests from mobile stations. This approach is adoptedin, for example, current third-generation mobile communication networks(FOMA service in NTT's Dokomo) and is disclosed in JP10-013904A. In thiscase, when a first-level packet transmission device has been reselectedso as to decrease link costs, a change also occurs in the layer-3address. Typically, when a layer-3 address is altered duringcommunication, communication applications that are based on TCP/IPprotocol such as Web browsing, file transfer, E-mail, and streamcommunication are interrupted even if the applications are beingexecuted. These problems can be avoided by either of the following twomethods:

1. Using Mobile IP that is stipulated in RFC3220 of IETF, the home agentis arranged outside the mobile communication network. This approachallows the continuation of communication by using fixed HOME addressesfor layer 4 and above while altering layer-3 “Care-of” addresses.

2. An operation is performed for switching higher-level packettransmission devices only for mobile stations that are not communicatingdata without implementing operations for switching higher-level packettransmission devices for mobile stations that have actually establishedradio links and that are in the process of communicating data. Theinstantaneous interruption of data communication that is caused byalteration of layer-3 addresses affects only mobile stations that arecommunicating data. Accordingly, for example, when mobile station 14 inFIG. 1 is in the process of communicating data, the communication iscontinued without change on packet transmission path P4. When the datacommunication has been completed, the path is switched to packettransmission path P5, and the next data communication is carried outusing packet transmission path P5. This approach can preventinstantaneous interruptions of communication to users without resortingto the previously described Mobile IP.

Although the preceding explanation regards embodiments of the presentinvention, the present invention is not limited only to theabove-described embodiments, but various additions and modifications canbe made. In addition, the functions possessed by the packet transmissiondevice of the present invention may of course be implemented byhardware, or can be implemented by a computer and a program for a packettransmission device. A packet transmission device program may beprovided by recording on a recording medium that can be read by acomputer such as a magnetic disk or semiconductor memory, may be readinto a computer upon start-up of the computer, and may then cause thecomputer to function as the packet transmission device in each of thepreviously described embodiments by controlling the operations of thecomputer.

1. A first network node in a mobile communication system, the firstnetwork node comprising: at least one processor; and at least one memorycoupled to the at least one processor, the at least one memory storinginstructions that when executed by the at least one processor cause theat least one processor to: receive, from a mobile station, a pathestablishment request message including type information that is not aname or an address of a node that is to be connected, the typeinformation comprising either: a first type indicating that the mobilestation requests to establish a first path, or a second type indicatingthat the mobile station requests a second path, employ a selectionmethod that selects a second network node based on an Access Point Name(APN), determine whether the type information indicates the first typeor the second type, and transfer at least a part of the pathestablishment request message to the second network node using theselection method, when the first network node determines that the typeinformation indicates the first type.
 2. The first network nodeaccording to claim 1, wherein the instructions stored in the at leastone memory further comprise instructions that when executed by the atleast one processor, cause the at least one processor to transfer atleast the part of the path establishment message to a third network nodenot using the selection method, when the first network node determinesthat the type information indicates the second type.
 3. A communicationmethod of a first network node in a mobile communication system, themethod comprising: receiving, from a mobile station, a pathestablishment request message including type information that is not aname or an address of a node that is to be connected, the typeinformation comprising either: a first type indicating that the mobilestation requests to establish a first path, or a second type indicatingthat the mobile station requests a second path; employing a selectionmethod that selects a second network node based on an Access Point Name(APN); determining whether the type information indicates the first typeor the second type; and transferring at least a part of the pathestablishment request message to the second network node using theselection method, when the first network node determines that the typeinformation indicates the first type.
 4. The method according to claim3, further comprising: transferring at least the part of the pathestablishment message to a third network node not using the selectionmethod, when the first network node determines that the type informationindicates the second type.
 5. A mobile station in a mobile communicationsystem, the mobile station comprising: at least one processor; and atleast one memory coupled to the at least one processor, the at least onememory storing instructions that when executed by the at least oneprocessor cause the at least one processor to: store type informationthat is not a name or an address of a node that is to be connected, thetype information comprising either: a first type indicating that themobile station requests to establish a first path, or a second typeindicating that the mobile station requests a second path, send a pathestablishment request message including the type information to a firstnetwork node that determines whether the type information indicates thefirst type or the second type, and receive a response message from thefirst network node via a base station, the first network node selectinga second network node based on an Access Point Name (APN) when the firstnetwork node determines that the type information indicates the firsttype.
 6. The mobile station according to claim 5, wherein the firstnetwork node selects a third network node when the first network nodedetermines that the type information indicates the second type.
 7. Acommunication method of a mobile station in a mobile communicationsystem, the method comprising: storing type information that is not aname or an address of a node that is to be connected, the typeinformation comprising either: a first type indicating that the mobilestation requests to establish a first path, or a second type indicatingthat the mobile station requests a second path; sending a pathestablishment request message including the type information to a firstnetwork node that determines whether the type information indicates thefirst type or the second type; and receiving a response message from thefirst network node via a base station, the first network node selectinga second network node based on an Access Point Name (APN) when the firstnetwork node determines that the type information indicates the firsttype.
 8. The method according to claim 7, wherein the first network nodeselects a third network node when the first network node determines thatthe type information indicates the second type.